The present invention relates to a plasma process apparatus for processing a semiconductor wafer or such other substrates with plasma, and the processing method.
The plasma process apparatus is a facility formed of a hermetically sealed space in which electrodes are provided. An object of processing, such as a substrate for semiconductor devices, is placed on the electrode, and a plasma discharge is provided in an atmosphere of reduced pressure for cleaning or etching the substrate, or depositing a certain specific layer on the substrate. The plasma discharge accompanies a heat generation; as a result, temperature of a substrate increases in the course of plasma processing. In an extreme case when the temperature rose to an extremely high level, the substrate could be burnt or broken due to thermal damage. In order to prevent this to happen, plasma process apparatus is normally provided with a cooling system intended to prevent a substrate from going too high temperature by cooling the electrode.
However, in a case where the object of plasma processing is a thin substrate whose thickness is very small relative to the area space, the substrate may easily cause a bowing when the temperature goes high. Then, part of the substrate lifts off the surface of electrode during plasma processing, which generates a gap between substrate and electrode. Once such a gap is generated, heat transmission from the substrate to the electrode is blocked, or the cooling effects can not reach the substrate despite the electrode is being cooled. Under such a situation, temperature of the substrate continues to go up and the substrate will suffer from thermal damage. Furthermore, abnormal discharge generated across the gap affects the evenness of plasma treatment.
Proving a mechanical pressure on substrate at the circumference edge has been one of the commonly employed countermeasures for preventing the bowing. For example, Japanese patent laid-open No. 211703/1995 (conventional technology) discloses a method, in which a silicon wafer 1 placed on a specimen electrode 3 is mechanically pressed down at the edge by a specimen holding device 4. Such a method, however, does not work well to suppress the lifting of silicon wafer at the central portion. Providing an electrostatic sucking device (electrostatic chuck) on the electrode could be a solution. However, cost of such device is rather high, which in turn invites a high production cost.
The present invention aims to offer a plasma process apparatus, as well as a method for the plasma process, with which a substrate can be cooled effectively during plasma processing, thermal damage is avoided, and an even treatment by plasma is provided.
With a plasma process apparatus of the present invention, a substrate is provided integrally on the bottom surface with a support member whose thermal expansion coefficient is greater than that of the substrate, which plasma process apparatus comprises substrate holding means for making contact with and pressing at the circumference edge the substrate, which is placed on an electrode with the support member down, onto the electrode from above, and cooling means for cooling the electrode.
In practice, a resin sheet is used for the above-described support member, and a semiconductor wafer is used for the substrate.
A plasma process apparatus of the present invention features in that it handles a substrate that is a semiconductor substrate bearing a circuit pattern formed on the front surface and a support member is attached on the front surface of the semiconductor substrate. The semiconductor substrate is placed on an electrode to be undergoing a plasma processing at the reverse surface.
In the present plasma process apparatus, the substrate holding means presses a substrate onto the electrode with a force that allows the substrate and the support member to make thermal expansion/shrinkage.
In a plasma process method of the present invention, a substrate is provided integrally at the bottom surface with a support member whose thermal expansion coefficient is greater than that of the substrate. The plasma process method comprises the steps of placing the substrate on the upper surface of an electrode with the support member down, pressing the substrate at the circumference edge onto the electrode, and generating plasma in a process chamber by applying a high frequency voltage to the electrode, while it is being cooled.
Practically, a resin sheet is used for the above-described support member attached on the bottom surface of the substrate, and a semiconductor wafer is used for the substrate.
In a plasma process method of the present invention, the substrate is a semiconductor substrate bearing a circuit pattern formed on the front surface and the support member is attached on the front surface of the semiconductor substrate. The semiconductor substrate is placed on the electrode to be processed with plasma at the reverse surface.
In the present plasma process method, the substrate is pressed at the circumference edge with a force that allows the substrate and the support member to make thermal expansion/shrinkage.
Method of the present invention is suitable especially to manufacturing of semiconductor devices. Based on the present method, thinner semiconductor devices may be implemented.
Under the above-described setup, where a substrate is fixed at the bottom surface with a support member and the substrate is processed by plasma while it is being pressed by substrate holding means, which is making contact at the circumference edge, onto the electrode, a force caused by thermal deformation of the substrate having the support member is converted into a force that exerts to have the substrate adhere closer to the electrode surface. Thus the simple method is effective in preventing the lifting up of a substrate due to thermal deformation.